A wide variety of known medical devices can be implanted within a patient's body to provide interventional or remedial treatments. Occlusion devices, for example, can be implanted to close perforations in septa, conduits, or ostia. An atrial septal defect in the heart, which is an abnormal opening in the septum between the left and right atria of the heart, is one such condition that can be treated by implanting an occlusion device to close the abnormal opening. Stent grafts provide another example of a class of implantable medical devices. A stent graft can be a generally tubular device, typically constructed of fabric that is mechanically supported by a relatively rigid structural framework called a stent frame. Stent grafts are often used to treat weak points, known as aneurisms, in the vasculature of a patient. For example, an abdominal aortic aneurism (“AAA”) is a localized dilation of the wall of the aorta in the abdominal region. A stent graft can be used to treat an AAA condition by being deployed within the aorta to act as a lining that traverses the aneurism; to reduce the stress on the aneurism caused by normal blood pressure and flow by permitting blood flow to bypass the aneurism, which may prevent a potentially deadly rupture of the aneurism. Many other types of known medical devices can be also implanted in patients to treat a wide variety of maladies.
Once deployed to the desired position within a patient, the ongoing efficacy of implantable devices can often depend on their ability to remain in an approximately fixed position relative to the surrounding tissue. For example, an occlusion device implanted to occlude or close an aperture should maintain its proper position relative to the tissue surrounding the aperture, or it may fail to close the aperture. Similarly, an AAA stent graft implanted to relieve stress on an aneurism should maintain its proper position as a lining within the aorta to traverse the AAA.
Fixation anchors or hooks can help perform the important function of securing an implantable medical device to the surrounding tissue and maintaining the device in proper position. In some cases, other parts of the device, such as a stent frame, can supply a force that presses the fixation anchors into contact with the tissue. Often, a fixation anchor includes a relatively sharp point like an arrow or a hook that is designed to penetrate the tissue. In some cases, a fixation anchor does not include a sharp point, and is intended to contact the tissue without penetrating it.
Currently, an increasing number of implantable medical devices are deployed using minimally invasive techniques. In such cases, the medical device is typically configured in a collapsed arrangement and delivered to the internal deployment site via a delivery catheter or sheath. At the deployment site, the medical device is ejected from the catheter and it expands to a larger size to effectively treat the particular medical condition. In many cases the minimally invasive delivery techniques require the medical device to be constructed from a frame that is resilient and compliant enough to be compressed into the lumen of a delivery catheter without causing permanent deformation to the device. When fixation anchors are included as an integral part of an implantable medical device, the fixation anchors must collapse with the frame to fit within the lumen of a delivery catheter.